Since St. Louis encephalitis virus (SLEV) was recognized in Houston in 1964, Houston has remained endemic, and occasionally epidemic, with flavivirus activity. The area is ecologically conducive to maintaining vector and virus activity. In 2002, West Nile virus (WNV) was identified in the Houston metropolitan area, resulting in 105 confirmed or probable human cases. Nationally, 4,156 WNV-positive cases were reported to the Centers for Disease Control and Prevention (CDC) that same year. During the 2003 transmission season, another 49 human cases were identified in Houston. The first objective of this proposal is to describe the clinical spectrum of illness and natural history of infection in both adults and children identified through surveillance. The second objective is to determine the rate of recovery and estimate the frequency of physical and mental sequelae as a result of infection. The third objective is to determine significant risk factors associated with progressing to encephalitis and/or death using case controls studies. We will be testing the hypothesis that history of hypertension or hypertension-inducing drugs and immunosuppressing conditions are associated with the development of severe disease. Additionally, blood specimens will be used to further examine the role of single nucleotide polymorphisms (SNP) in oligoadenylate synthase (OAS) genes as a genetic susceptibility factor predisposing an individual to severe disease. Finally, we will characterize the host immunologic response. Obtaining these objectives will provide us with a better understanding of the clinical aspects of a virus that will continue to persist and cause human illness in the United States, and allow us to identify and target interventions for populations at risk for encephalitis and death. The candidate is a veterinarian and Assistant Professor of Epidemiology at the University of Texas School of Public Health in Houston. Before taking this position, she received applied epidemiology training through the Epidemic Intelligence Service (EIS) at CDC, and was part of the investigation team of the WNV outbreak in New York City in 1999. She is currently working on her PhD in Preventive Medicine and Community Health, Clinical Science Curriculum at the University of Texas Medical Branch. Her time will be directed toward completion of the specific aims of this proposal and her PhD. [unreadable] [unreadable] [unreadable]